1. Field of the Invention
The present invention relates to an air conditioner having two internal refrigerating-cycle heat exchangers in an air-conditioning housing for air dehumidification, and more particularly to an improved air conditioner which is capable of enhancing controllability of blowout air temperature in a dehumidifying operation mode.
2. Description of Related Art
A conventional automotive air conditioner having a dehumidifying-mode setting is disclosed in Japanese Unexamined Publication No. 40056/1996. The conventional air conditioner is arranged to make it possible to set up a dehumidifying operation mode by means of a refrigerating cycle system comprising an internal condenser and an internal evaporator in an air-conditioning housing, and an external heat exchanger outside the air-conditioning housing.
In the dehumidifying mode, a refrigerant flows through the internal condenser, the external heat exchanger and then the internal evaporator. In the internal evaporator, air is cooled and dehumidified. The cooled and dehumidified air is then heated in the internal condenser.
In this sequence of dehumidification, in which the air is cooled and dehumidified sufficiently in the internal evaporator, heating performance of the internal condenser is controlled to regulate a temperature of air passing through the internal condenser (condenser outlet temperature) corresponding to a blowout temperature of conditioned air.
More specifically, in the above-mentioned conventional arrangement, a temperature of air immediately after passing through the internal evaporator (evaporator outlet temperature) is made lower than a suction temperature of air before passing through the internal evaporator by a degree of at least a predetermined value. The above is accomplished by controlling compressor rotational speed to provide a required level of air cooling and dehumidification.
The condenser outlet temperature is regulated by controlling a restriction opening of variable flow restriction means (electric expansion valve), equipped between the external heat exchanger and the internal condenser, to provide a required blowout temperature TAO as calculated according to various air-conditioning environmental factors (e.g., inside air temperature, outside air temperature, etc.).
However, it has been found that the conventional arrangement mentioned above has several disadvantages. In the conventional air conditioner mentioned above, when a user adjusts a blowout temperature setting lever for regulating the condenser outlet temperature, the blowout temperature TAO is recalculated accordingly. The restriction opening of the variable flow restriction means is then varied in small increments so that the condenser outlet temperature reaches a target value corresponding to the required blowout temperature TAO. Since the restriction opening is varied in small increments as stated above, the conventional air conditioner is disadvantageous in that a response characteristic of the condenser outlet temperature is typically slow, and thus unsatisfactory.
It may be possible to regulate the condenser outlet temperature quickly by varying the restriction opening in larger increments. However, if the restriction opening is varied in such a manner, refrigerant flow rate varies significantly, causing an overshoot or undershoot condition of the condenser outlet temperature with respect to the target blowout temperature TAO.